The area between the sealing edge and the shaft is the most important. The sealing effect is achieved by pre-loading the sealing lip, making its internal diameter slightly smaller than the shaft diameter. The garter spring ensures constant pressure and maintains the radial force to the shaft, flattening the sealing edge to a defined width. Underneath the flattened area a thin fluid film is formed. Its thickness must be between 1 and 3um to avoid a leakage. The meniscus acts as an interface between the outside air and the fluid. Any break in the meniscus will result in leakage. This can occur if the shaft contains scratches along the seal path.